Imagine every time you hear the word chair, your mouth fills with the taste of strawberries. Or to you, Tuesdays are red and the letter T is male, light blue, trustworthy and loyal. Sound strange? Welcome to the fascinating world of synaesthesia.

For some people, every letter has a specific colour.  Image credit: Stephen Lock via Flickr

Blended senses

If someone scratches a blackboard with his or her nails, I taste iron. The intro of “Time” by Pink Floyd is golden yellow and blue.   One synaesthete’s experiences

Scientists have known about synaesthesia (literally ‘union of the senses’) for more than 200 years. Synaesthetes – people who have synaesthesia – experience an unusual blending of the senses. Once dismissed as an imaginary condition, synaesthesia is currently a hotbed of scientific research.

In synaesthesia, the stimulation of one sense (for example hearing a sound) brings about an additional experience in the same or another sense (for example seeing a colour). There are about sixty different forms of synaesthesia and around half of all synaesthetes have more than one kind of synaesthesia.

For many years, synaesthesia was considered to be made-up and not taken seriously by the scientific world. But over the past 30 or so years research has shown synaesthesia is a real neurological condition.

A colourful world

The most common form of synaesthesia is known as grapheme-colour synaesthesia. People with this condition experience colours when viewing written letters or numbers. The colour may be seen in the ‘mind’s eye’ or simply perceived as associated with the letter or number. For example, the days of the week or months of the year are inherently coloured and these synaesthetes have extremely specific coloured alphabets.

Grapheme-colour synaesthetes still see letters printed in the actual colour they appear on the page but simultaneously perceive different colours associated with each one. Six-year old children already have some of these specific colour associations.

In a different kind of synaesthesia, colours are evoked by particular sounds. For example, middle C on the piano may be experienced as lime green and the sound of a door opening a bright crimson.

Another form of synaesthesia – lexical-gustatory synaesthesia – involves words evoking a specific taste in the mouth. One man explained to researchers the word safety tastes like ‘toast lightly buttered’ and Phillip like ‘oranges not quite ripe’.

An extraordinary but rare form of synaesthesia is called mirror-touch synaesthesia. For a person with this kind of synaesthesia, just seeing someone else’s cheek being touched leads to the sensation their own cheek is being touched. Mirror-touch synaesthetes report feeling the pain being experienced by another person.

Are you a synaesthete?

Over the years, estimates of people with synaesthesia have ranged from 1 in 20 people up to 1 in 250,000. Some forms of the condition are much more common than others with about 1 in 500 people experiencing grapheme-colour synaesthesia but only 1 in 25,000 people experiencing sound-odour synaesthesia. And these figures are hard to come by because many synaesthetes do not realise their experiences are any different to ‘normal’. Want to find out if you’re a synaesthete?

A key characteristic of synaesthesia is that the experiences are involuntary, present since childhood and always fixed for life. (One of the key differences between synaesthesia and drug-induced hallucinations is the pairings in synaesthetes never change). And you either have it or you don’t. Synaesthesia runs in families indicating a genetic component to the condition. A study published earlier this year found among families with sound-colour synaesthesia, gene variations may result in unusually high numbers of nerve connections in particular parts of the brain.

Other research suggests at least one kind of synaesthesia may be partly learned and involve memories. A study published in 2013 described 11 individuals whose letter-colour associations matched closely with the colours of the very popular letter magnets that may well adorn your fridge.

A study of more than 6,500 American synaesthetes found 6% have colour associations that match the fridge magnets. This figure goes up to 15% if you only consider those synaesthetes born in the decade after the magnets started being produced. Of course, it may be only people who already have synaesthesia learn these colour associations.

Definitely not a disorder

The jury is still out when it comes to what causes synaesthesia but evidence is mounting that the brains of synaesthetes have increased neural connections between the areas associated with different senses. Interestingly, people with autism are three times more likely to experience synaesthesia than non-autistic people.

Regardless of the cause, one thing is clear: synaesthesia is not a disorder. Synaesthetes report many advantages to the condition, for example having additional cues to remember dates and phone numbers. Synaesthesia seems to be more prevalent among artists, writers and musicians and there’s evidence synaesthetes may be better at certain types of creative thinking.

Importantly, most synaesthetes like having synaesthesia.

If you ask synaesthetes if they’d wish to be rid of it, they almost always say no. For them, it feels like that’s what normal experience is like. To have that taken away would make them feel like they were being deprived of one sense.
Simon Baron-Cohen, synaesthesia researcher at the University of Cambridge

To top it all off, recent research has found training non-synaesthetes to have letter/ number-colour associations may be a great idea. It can help to ward off the cognitive decline that occurs in the early stages of dementia and to assist people recovering from brain injuries.

Perhaps those of us not lucky enough to be synaesthetes should spend more time playing with fridge magnets to learn some colour associations.

Links and stuff

• An eyeful of sound – short documentary
• What colour is Tuesday? Ted Ed video explaining synaesthesia
• Melbourne University researcher Solange Glasser talking about her research
• Synaesthesia researcher Anina Rich (Macquarie University) talking about her research